Ch. 11 Flashcards
Why is the one-group, pretest/posttest design a really bad experiment?
- it has only one group, not two. There is no comparison group
- there are 6 potential internal validity threats because of this: maturation threat, history threat, regression threat, attrition threat, testing threat, instrumentation threat
Maturation Threat
A change in behavior that emerges more or less spontaneously over time.
(People adapt to changed environments; children get better at walking and talking; plants grow taller—but not because of any outside intervention. It just happens.)
History Threat
Result from a “historical” or external factor that systematically affects most members of the treatment group at the same time as the treatment itself, making it unclear whether the change is caused by the treatment received. To be a history threat, the external factor must affect most people in the group in the same direction (systematically), not just a few people (unsystematically).
Regression Threat
Refers to a statistical concept called regression to the mean. When a group average (mean) is unusually extreme at Time 1, the next time that group is measured (Time 2), it is likely to be less extreme—closer to its typical or average performance.
(see p.316 in text)
Attrition Threat
Becomes a problem for internal validity when attrition is systematic; that is, when only a certain kind of participant drops out.
Testing Threat
A specific kind of order effect, refers to a change in the participants as a result of taking a test (dependent measure) more than once. People might have become more practiced at taking the test, leading to improved scores, or they may become fatigued or bored, which could lead to worse scores over time.
Instrumentation Threat
When a measuring instrument changes over time. In observational research, the people who are coding behaviors are the measuring instrument, and over a period of time, they might change their standards for judging behavior by becoming more strict or more lenient.
Observer Bias
Occurs when researchers’ expectations influence their interpretation of the results.
Demand characteristics
Are a problem when participants guess what the study is supposed to be about and change their behavior in the expected direction.
Double-blind study
Designed to prevent observer bias and demand characteristics. A design in which neither the participants nor the researchers who evaluate them know who is in the treatment group and who is in the comparison group.
Masked Design
When a double-blind study is not possible, a masked (blind) design is an alternative. In this design, participants know which group they are in, but the observers do not.
Placebo effect
Occurs when people receive a treatment and really improve—but only because the recipients believe they are receiving a valid treatment.
Double-blind placebo control study
One group receives the real drug or real therapy, and the second group receives the placebo drug or placebo therapy. Crucially, however, neither the people treating the patients nor the patients themselves know whether they are in the real group or the placebo group.
Null effect
Also known as null result
When results indicate there is no significant covariance between IV and DV.
(It might be the case that the independent variable really does not affect the dependent variable; however, might be that there is covariance but that the study was not designed or conducted carefully enough to detect it.)
Weak manipulations
When not enough difference between two conditions.
Might prevent study results from revealing a true difference that exists between two or more experimental groups.
When you interrogate a null result, it’s important to ask how the researchers operationalized the independent variable. In other words, you have to ask about construct validity.
